The key is keep the starting batts completely isolated from the house loads when the motors are shut down. To get the charging abilities of the alternators to the house batts can be done with either a BEP VSR (voltage sensative relay), a Blue Seas ACR (Automatic charging relay), or a Yandina Combiner. They all work basically the same way, when a charging presence is sensed, and the output voltage is high enough, the relays open and combine the batts to send amperage to all. Remove the increased voltage source, and they shut, isolating the batts...
